Many people believe that the healthiest diet is simply one that avoids ultra-processed foods.
However, a large new study suggests that the overall nutritional quality of what we eat may be much more important than how processed the food is. The findings challenge a growing belief that all processed foods are harmful.
The study was led by researchers from the Harvard T.H. Chan School of Public Health and included information from more than 200,000 adults who were followed for several decades.
The researchers wanted to separate two ideas that are often mixed together: food processing and nutritional quality.
Many ultra-processed foods are high in sugar, salt, and unhealthy fats, so they are often linked with poor health. However, some processed foods, such as whole-grain breakfast cereals, fortified plant-based milk, canned beans, and whole-grain bread, can also provide fibre, vitamins, minerals, and other important nutrients.
To better understand the issue, the researchers compared healthy and unhealthy plant-based diets while also considering whether the foods were minimally processed or ultra-processed. This allowed them to examine whether processing itself affected long-term health.
During the study, many participants developed heart disease or type 2 diabetes or died. People who ate high-quality diets consistently had a lower risk of these health problems. Those with poor-quality diets had a much higher risk.
Interestingly, the amount of food processing made very little difference within each diet quality group. Healthy diets remained healthy whether they included some processed foods or mostly minimally processed foods. Likewise, unhealthy diets remained linked to poorer health even when they contained mostly minimally processed foods.
This finding highlights an important weakness in food classification systems that judge foods mainly by processing. Some nutritious foods can be labelled ultra-processed, while some minimally processed foods, such as refined grains or sugary homemade desserts, may still have limited nutritional value.
The researchers believe dietary advice should continue to focus on eating more vegetables, fruits, legumes, whole grains, nuts, and healthy plant oils. Choosing nutrient-rich foods appears to matter more than avoiding every processed product.
The findings may also encourage food manufacturers to improve the nutritional quality of packaged foods. Better ingredients, lower salt and sugar levels, and higher fibre content could make convenient foods healthier for busy families.
This research provides valuable evidence because it followed a very large number of people over many years.
However, it was an observational study, meaning it cannot prove cause and effect. In addition, the findings were presented at a scientific meeting and should be considered preliminary until fully peer reviewed.
Even so, the results reinforce decades of evidence showing that overall dietary quality remains one of the strongest predictors of long-term health.
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